The present invention relates to embodiments of a controller and method for monitoring trailer brake applications. In a tractor-trailer commercial vehicle, the driver of the vehicle actuates the foot brake pedal to apply the service brakes on both the tractor and the trailer. If the driver desires to apply only the brakes on the trailer, he can actuate a trailer control brake valve in the cab of the tractor, such as the TC-7™ trailer control brake valve from Bendix Commercial Vehicle Systems LLC of Elyria Ohio. When he actuates the trailer control brake valve, the service brakes of the trailer are applied, but the service brakes of the tractor remain released. Application of the trailer control brake valve is not intended to replace a service brake application using the foot brake pedal. However, some drivers overuse the trailer control brake valve in an effort to save service brake life on the tractor at the expense of the trailer service brakes. Therefore, there is a need to monitor the use of the trailer service brakes while monitoring the use of the tractor service brakes to ensure the trailer service brakes are not being used more often than the tractor service brakes.